A solid oxide fuel cell (hereinafter, referred to as SOFC) has been known as a fuel cell of high efficiency to be widely used. Because the SOFC has a high operating temperature to increase ionic conductivity, the SOFC can use air discharged from a compressor of a gas turbine as air (oxidant) supplied to the side of an air electrode (cathode). In addition, an unused high-temperature fuel and waste heat exhausted from the SOFC can be used as fuel and an oxidant in the combustor of the gas turbine. Further, other than the SOFC, a molten carbonate fuel cell is known as a fuel cell having a high operation temperature, and, similarly to the SOFC, the use of waste heat thereof in cooperation with a gas turbine has been examined.
For this reason, for example, as described in the following Patent Literature 1, various systems in which the SOFC, the gas turbine, and the steam turbine are combined, have been suggested as power generation systems that can achieve power generation of high efficiency. In combined systems described in Patent Literatures 1 and 2, the SOFC and the gas turbine having the gas turbine combustor burning exhausted fuel gas and exhausted air discharged from the SOFC and the compressor compressing air and supplying the air to the SOFC are provided.
The combined system described in Patent Literature 1 has a fuel gas flow line that supplies fuel gas output from the SOFC (fuel cell) to the combustor and a combustible gas bypass flow line that supplies combustible gas generated in the system to the fuel gas flow line and controls an amount of combustible gas supplied from the combustible gas bypass flow line to the fuel gas flow line to make a calorific value in an inlet of the combustor of the gas turbine constant. In addition, in Patent Literature 2, in the combined system including the SOFC (fuel cell) and the gas turbine, a plurality of fuel systems supplying fuel to the gas turbine are provided and a flow rate of each system is adjusted.